Analyze This: Flu vaccine’s protection varies | Science News for Students

Analyze This: Flu vaccine’s protection varies

A flu shot can’t totally prevent you from getting sick — still, a yearly shot makes good sense
Jan 10, 2018 — 6:30 am EST
sick teen
Getting the flu is no fun, but a yearly vaccine can help keep you from getting sick.

Every winter, flu season rolls around. Ads telling you to get your flu shot show up everywhere. Vaccination may not seem that important. But influenza is more than just a bad cold. In the United States alone, it can kill several thousand people in any given year — and sometimes tens of thousands. Those most at risk of side effects (including death) are the very young and very old. Getting a flu shot makes sense even for people at low risk, however. Not only can they protect you, but they also limit your ability to spread the infection to vulnerable people around you.

Unfortunately, getting a shot won’t guarantee you can’t come down with the flu. That’s because the vaccine is never 100 percent effective. What’s more, how well it works can vary widely from one year to the next. The reason? A vaccine is only created to protect against a few strains of flu virus. Months before each flu season, the World Health Organization recommends three or four strains to include in the coming year’s vaccine. Each country then decides which of those strains it will target in its vaccine. In the United States, the Food and Drug Administration has the final word. If this agency guesses right and the strains in the vaccine match those spreading around the most people, the vaccine can be especially effective.

Even during a good year, though, that might not mean everyone who gets a shot will stay healthy. During the 2015-2016 flu season, for instance, only about half of all people who got a vaccination were protected. That’s the finding of a study in the August 10 New England Journal of Medicine.

A team of doctors looked at people at least 6 months old who had been vaccinated during the 2015-2016 flu season. Some received vaccines that had a “live” virus. (This vaccine is safe and won’t give someone the flu because the virus has been weakened.) Others were given vaccines that had an inactive (or “killed”) form of the virus.

The new data now show that the type of vaccine proved particularly important in how well it protected young people. Among children ages 2 to 17, the inactive virus was much more effective. It protected 12 in every 20 kids that got a flu shot. The one that used a live virus, in contrast, protected only one in every 20 kids. As a result, the U.S. Advisory Committee on Immunization Practices recommended not using live-virus vaccines this year.

flu vaccine effectiveness
Vaccine makers must anticipate months in advance which strains of flu will dominate each year. In some seasons, such as in 2014-2015, the vaccine’s effectiveness was low. That means a large share of people who got the shot still came down with the flu.
E. Otwell

Data Dive: 

  1. What is the approximate percent (%) effectiveness of flu vaccines in each year from 2004 to 2016? Round your answer to the nearest 5 percent.
  2. Make a list of the values shown in the graph, putting them in order from the lowest to highest. Identify the median for this data set, and calculate the mean (also known as average). Count how many numbers are in your data set and divide the list into quartiles (four equal parts). Now create a box and whisker plot (a diagram that displays the distribution of data) by drawing a line long enough to contain all of your data, marking numbers at even intervals along the line. Next, mark the median on the line you just drew, along with the upper and lower quartiles. Make a box by drawing horizontal lines connecting the quartiles. Then mark the endpoints (the numbers with the lowest and highest values in your data).
  3. Looking at the shape of the plot you created, what can you tell about the spread of those data (are the data evenly spread out, or do they clump somewhere)? Hint: determine the range (difference between the highest and lowest values) in each quartile.
  4. What does the spread of the data in the bar graph tell you about the general trend of how well vaccines worked between 2004 and 2016 (their percent effectiveness)?
  5. Compare the mean and median for this set of data. If there are outliers, will the mean or median better represent the general trend in those data? Explain.
  6. According to the text above, why does how well a vaccine works (its percent effectiveness) vary each year?
  7. Critique the graph. What would you do differently? What information do you feel could be added to the graph to make it more useful or easier to understand?

Analyze This! explores science through data, graphs, visualizations and more. Have a comment or a suggestion for a future post? Send an email to

Power Words

(more about Power Words)

ad     Short for advertisement. It may appear in any medium (print, online or broadcast) and has been prepared to sell someone on a product, idea or point of view.

data     Facts and/or statistics collected together for analysis but not necessarily organized in a way that gives them meaning. For digital information (the type stored by computers), those data typically are numbers stored in a binary code, portrayed as strings of zeros and ones.

influenza     (also known as flu) A highly contagious viral infection of the respiratory passages causing fever and severe aching. It often occurs as an epidemic.

journal     (in science) A publication in which scientists share their research findings with experts (and sometimes even the public). Some journals publish papers from all fields of science, technology, engineering and math, while others are specific to a single subject. The best journals are peer-reviewed: They send all submitted articles to outside experts to be read and critiqued. The goal, here, is to prevent the publication of mistakes, fraud or sloppy work.

mean     One of several measures of the “average size” of a data set. Most commonly used is the arithmetic mean, obtained by adding the data and dividing by the number of data points.

median     (in mathematics) The value or quantity that lies at the midpoint of a group of numbers that had been listed in order from lowest to highest.

outlier     (in statistics) An observation that lies outside the general range of the rest of the data.

quartile     Values that divide a list of numbers into quarters or fourths. Scientists also often refer to each individual fourth as a quartile.

range   The full extent or distribution of something. For instance, a plant or animal’s range is the area over which it naturally exists. (in math or for measurements) The extent to which variation in values is possible. Also, the distance within which something can be reached or perceived.

risk     The chance or mathematical likelihood that some bad thing might happen. For instance, exposure to radiation poses a risk of cancer. Or the hazard — or peril — itself. (For instance: Among cancer risks that the people faced were radiation and drinking water tainted with arsenic.)

strain     (in biology) Organisms that belong to the same species that share some small but definable characteristics. For example, biologists breed certain strains of mice that may have a particular susceptibility to disease. Certain bacteria or viruses may develop one or more mutations that turn them into a strain that is immune to the ordinarily lethal effect of one or more drugs.

Food and Drug Administration (or FDA)     A part of the U.S. Department of Health and Human Services, FDA is charged with overseeing the safety of many products. For instance, it is responsible for making sure drugs are properly labeled, safe and effective; that cosmetics and food supplements are safe and properly labeled; and that tobacco products are regulated.

vaccine     (v. vaccinate) A biological mixture that resembles a disease-causing agent. It is given to help the body create immunity to a particular disease. The injections used to administer most vaccines are known as vaccinations.

virus     Tiny infectious particles consisting of RNA or DNA surrounded by protein. Viruses can reproduce only by injecting their genetic material into the cells of living creatures. Although scientists frequently refer to viruses as live or dead, in fact no virus is truly alive. It doesn’t eat like animals do, or make its own food the way plants do. It must hijack the cellular machinery of a living cell in order to survive.


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Further Reading

Journal: M.L. Jackson et al. Influenza vaccine effectiveness in the United States during the 2016-2016 season. New England Journal of Medicine. Vol. 377, p. 534. August 10, 2017doi: 10.1056/NEJMoa1700153.